Liquid crystal display panel and liquid crystal display device

ABSTRACT

A liquid crystal display panel includes switching elements, transparent pixel electrodes, and a transparent common electrode having a predetermined area overlapped with an upper layer of the transparent pixel electrode through an insulating film and driving liquid crystal with the transparent pixel electrode. In plane view, a shading layer covers at least one part of a conductive pattern where a light leakage occurs in front view by an alignment defect of the liquid crystal near a non-permeable conductive pattern disposed in the display region at the time of black display, and has eaves more protruding than the conductive pattern. The transparent common electrode is provided to overlap with the conductive pattern arranged to overlap with the light-shielding layer having the eaves in a side of the liquid crystal and to protrude compared with the light-shielding layer having the eaves in a planar view.

INCORPORATION BY REFERENCE

This application is a Continuation of U.S. patent application Ser. No.13/251,613, filed Oct. 3, 2011, and is based upon and claims the benefitof priority from Japanese Patent Application No. 2010-261948 filed inJapan on Nov. 25, 2010, the entire content of each of the foregoingapplications is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display panel and aliquid crystal display device. More specifically, the present inventionrelates to a liquid crystal display panel and a liquid crystal displaydevice of fringe field switching (FFS) type.

2. Description of Related Art

In recent years, in substitution for a conventional cathode-ray tube,new display devices having a thin flat-type display panel usingprinciples of liquid crystal, electroluminescence or the like have beenfrequently used. A liquid crystal display device which represents thesenew display devices has characteristics in that it can be driven with alow power voltage, in addition to its thinness and lightness. The liquidcrystal display device includes a liquid crystal layer disposed betweentwo substrates. One substrate is an array substrate forming a displayarea in which a plurality of pixels are arranged in matrix, and theother substrate is a color filter substrate.

In particular, in a thin film transistor (TFT)-type liquid crystaldisplay device, a TFT which is a switching element is provided in eachpixel on the array substrate, and each pixel is able to independentlycarry a voltage to drive a liquid crystal layer, thereby making itpossible to achieve the display of high quality with little crosstalk.Each pixel includes a gate line (scan line) that controls ON/OFF of theTFT, and a source line (signal line) for inputting image data. Eachpixel is typically formed in an area surrounded by the gate line and thesource line.

An In-Plane switching (IPS)-type liquid crystal display device has onearray substrate on which a plurality of pixel electrodes and commonelectrodes (opposed electrodes) are alternately arranged, so as to applya substantially-horizontal electric field to the substrate surface fordisplay. The IPS type liquid crystal display device has better viewangle property compared with a typical Twisted Nematic (TN) type.However, the conventional IPS-type liquid crystal display device has asmaller light transmission rate compared with that of the typical TNtype.

As a system in which this defect is improved, a fringe field switching(FFS) system has been suggested. The FFS-type liquid crystal displaydevice is the system of achieving the display by applying a fringeelectric field (an oblique electric field including both components of ahorizontal electric field and a vertical electric field) to a liquidcrystal layer. In the FFS-type liquid crystal display device, the pixelelectrode and the common electrode are formed on one array substrate asis similar to the IPS system. However, the pixel electrode and thecommon electrode are overlapped with each other with an insulation filminterposed therebetween. Typically, the lower electrode is a plateelectrode (the lower electrode may be a plurality of branch-likeelectrodes). Furthermore the upper electrode includes a comb-toothelectrode including a plurality of branch electrode parts electricallyconnected in common, and gap parts therebetween.

Both of the comb-tooth electrode and the plate electrode are formed oftransparent conductive films in the FFS system, thereby achievingparticularly high light transmission rate. In the FFS system, a liquidcrystal layer is driven by a fringe electric field between upper andlower electrodes, which makes it possible to drive a liquid crystallayer on a branch-like electrode part which is not a gap part of thecomb-tooth electrode as well. The pixel electrode and the commonelectrode are formed of transparent conductive films, which can improvea light transmission rate compared with the IPS system in which lightrarely transmits on the pixel electrode and the common electrode.

The FFS-type liquid crystal display device can be roughly divided intotwo structures. The first structure is that, on the array substrate, acommon electrode which is a common potential is formed of a plateelectrode arranged on the side of the lower layer, and a pixel electrodeinto which a pixel potential is written through a thin-film transistoris formed of a comb-tooth electrode arranged on a side of the upperlayer (e.g., Japanese Unexamined Patent Application Publication Nos.2002-31812 and 2005-234525). The second structure is that, on the arraysubstrate, a common electrode and a pixel electrode are opposite to thearrangement stated above. Specifically, the common electrode is formedof a comb-tooth electrode in the upper layer, and the pixel electrode isformed of a plate electrode in the lower layer (e.g., JapaneseUnexamined Patent Application Publication No. 2008-191669). JapaneseUnexamined Patent Application Publication No. 2003-322869 discloses astructure in which one of the two electrodes of the plate electrode andthe comb-tooth electrode is formed in the color filter substrate inplace of the array substrate.

In the second structure stated above, a black matrix is typicallyarranged only in order to prevent color mixture of adjacent pixels. Inother words, the black matrix having a width equal to or smaller thanthat of a source line is typically arranged on the source line. Thereason that this structure can be employed is that it is possible toshield the electric field from the source line by arranging thecomb-tooth electrode which is the common electrode on the source linewhile being overlapped with each other. In other words, this is becauseit is possible to prevent occurrence of a domain due to alignmentdisorder of liquid crystal due to an electric field from the sourceline. Further, Japanese Unexamined Patent Application Publication No.2008-191669 described above discloses the structure that does notinclude the black matrix itself. By employing such a structure, even apart just beside the source line can contribute to the display, whichcan improve the light transmission rate.

SUMMARY OF THE INVENTION

However, the present inventors have found that, in the liquid crystaldisplay device having the second structure of FFS type, the contrastdecreases around the source line. In short, it is desired to increasethe contrast in the recent liquid crystal display device. Whiledescribed above is the problem in the source line, the similar problemmay occur in a non-transparent conductive pattern formed in a displayarea.

The present invention has been made in view of the background describedabove. One object of the present invention is to provide a liquidcrystal display panel and a liquid crystal display device that arecapable of improving contrast.

A first exemplary aspect of the present invention is a liquid crystaldisplay panel including liquid crystal sealed between a first substrateand a second substrate, in which the first substrate includes: gatelines; source lines that are formed to cross the gate lines; switchingelements that are arranged near the intersections of the gate lines withthe source lines; pixel regions that are specified by the gate lines andthe source lines, the pixel regions being arranged in matrices;transparent pixel electrodes that are connected to the switchingelements; and a transparent common electrode that includes at leastbranch-like electrode parts and gap parts between the branch-likeelectrode parts, the transparent common electrode being arranged in anupper layer of the transparent pixel electrodes so that a predeterminedarea of the transparent common electrode is overlapped with thetransparent pixel electrode with an insulating film interposedtherebetween, the transparent common electrode being configured to drivethe liquid crystal with the transparent pixel electrode. In plane view,a shading layer covers at least one part of a conductive pattern where alight leakage occurs in front view by an alignment defect of the liquidcrystal near a non-permeable conductive pattern disposed in the displayregion at the time of black display, and has eaves more protruding thanthe conductive pattern. The transparent common electrode is provided soas to overlap with the conductive pattern overlapped with thelight-shielding layer having the eaves in a side of the liquid crystaland to protrude compared with the light-shielding layer having the eavesin a planar view.

The present invention achieves the excellent effect that it can providea liquid crystal display panel and a liquid crystal display device thatare capable of improving contrast.

The above and other objects, features and advantages of the presentinvention will become more fully understood from the detaileddescription given hereinbelow and the accompanying drawings which aregiven by way of illustration only, and thus are not to be considered aslimiting the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic plane view of a liquid crystal display panelaccording to a first exemplary embodiment;

FIG. 2 is an enlarged schematic plane view showing a main part of adisplay area of an array substrate according to the first exemplaryembodiment;

FIG. 3 is a cross-sectional view taken along the line of FIG. 2;

FIG. 4 is a schematic cross-sectional view of the liquid crystal displaypanel according to the first exemplary embodiment;

FIG. 5 is a schematic cross-sectional view of the liquid crystal displaypanel according to the first exemplary embodiment;

FIG. 6 is an explanatory view of alignment processing of the liquidcrystal display panel according to the first exemplary embodiment;

FIG. 7 is a graph in which measured values of a black luminance in afrontal direction are plotted with respect to a distance D1 of eaves ofa black matrix on a source line;

FIG. 8 is a schematic explanatory view for describing a cause of anincrease in the black luminance;

FIG. 9 is electrode position dependent calculation data of atransmission rate at a time of white display;

FIG. 10 is a transmission rate from an end part of the black matrix toan edge part of a common electrode with respect to a distance D2;

FIG. 11A is an explanatory view of absorption axes of a lower-sidepolarizing plate and an upper-side polarizing plate seen from a frontaldirection;

FIG. 11B is an explanatory view of absorption axes of the lower-sidepolarizing plate and the upper-side polarizing plate seen from anoblique direction;

FIG. 12 is a graph in which contrast is plotted with respect to a polarangle;

FIG. 13A is an explanatory view for describing the polar angle;

FIG. 13B is an explanatory view for describing an azimuth angle;

FIG. 14 is a schematic cross-sectional view of a liquid crystal displaypanel according to a second exemplary embodiment;

FIG. 15 is a graph in which contrast from a viewing direction of anazimuth angle of 45° and a polar angle of 45° is plotted with respect toa distance D1 in the liquid crystal display panel according to thesecond exemplary embodiment; and

FIG. 16 is an enlarged schematic plane view showing a main part of adisplay area of an array substrate according to a third exemplaryembodiment.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

Hereinafter, exemplary embodiments of the present invention will bedescribed as an example. The size and the ratio of each element in thedrawings are shown for the convenience of description, and are differentfrom the actual ones.

First Exemplary Embodiment

FIG. 1 is a schematic plane view for describing one example of a liquidcrystal display panel mounted on a liquid crystal display deviceaccording to a first exemplary embodiment of the present invention. Theliquid crystal display device includes a liquid crystal display panel100 of active matrix type in which an array substrate 1 which is a firstsubstrate is arranged opposite to a color filter substrate 2 which is asecond substrate with liquid crystal interposed therebetween. The arraysubstrate 1 includes gate lines, source lines, TFTs, pixel electrodes, atransparent common electrode supplied with a reference potential and thelike formed on a transparent substrate made of glass, plastic, or thelike. The color filter substrate 2 includes a color filter, a blackmatrix which is a light-shielding layer and the like formed on atransparent substrate made of glass, plastic, or the like.

The liquid crystal display panel 100 includes a display area 3 whichcontributes to a display, and a frame area 4 which is provided in anouter periphery of the display area 3. The frame area 4 includes gateline drive circuits 5 and source line drive circuits 6 mounted thereonby a Chip On Glass (COG) mounting technique. Further, in the end of thearray substrate 1, a plurality of terminals (not shown) are arranged. Inorder to supply various voltages, clocks, image data or the like to thegate line drive circuits 5 and the source line drive circuits 6, theplurality of terminals are connected to flexible substrates 7 and 8connected to an external circuit. Note that the gate line drive circuits5 and the source line drive circuits 6 may be integrated into one drivecircuit. Further, the flexible substrates 7 and 8 may be integrated intoone flexible substrate.

The liquid crystal display device contains the liquid crystal displaypanel 100 structured as stated above, a backlight unit (not shown) whichis a light source and the like in a housing. The backlight unit istypically arranged in a side opposite to a display surface. The displaysurface of the liquid crystal display panel 100 is contained so as to beviewed from inside the housing.

When an electric signal is externally input to the liquid crystaldisplay device including the liquid crystal display panel 100 asdescribed above, a drive voltage is applied to transparent pixelelectrodes 14 and a transparent common electrode 15, which changes thedirection of molecules of the liquid crystal according to the drivevoltage. Then, light emitted from the backlight unit is interrupted ortransmitted to an observer through the array substrate 1, the liquidcrystal, and the color filter substrate 2, thereby achieving display ofvideo or the like on the display surface of the liquid crystal displaypanel 100.

FIG. 2 is an enlarged schematic plane view showing a main part of thedisplay area 3 of the array substrate 1 according to the first exemplaryembodiment. FIG. 3 is a cross-sectional view taken along the line ofFIG. 2.

The array substrate 1 includes a transparent substrate 51 made of glass,plastic, or the like, gate lines 11, source lines 12, common lines 13,the transparent pixel electrodes 14 which are a plate electrode arrangedin the side of the lower layer, and a transparent common electrode 15which is a comb-tooth electrode arranged in the side of the upper layer.The array substrate 1 further includes TFTs 20, gate electrodes 21,source electrodes 22, drain electrodes 23, a gate insulating film 31, asemiconductor film 32, an ohmic contact film 33 and the like.

As shown in FIG. 2, the gate line 11 extends in a lateral direction anda plurality of gate lines 11 are arranged in a vertical direction. Thecommon line 13 is formed in parallel to the gate line 11 in the samelayer as the gate line 11 (see FIG. 2). The common line 13 serves tosupply a reference potential to the transparent common electrode 15.Each of the gate line 11 and the common line 13 can be formed of asingle layer film of metal (e.g., Al, Cr, Mo, Ti, Ta, W, Ni, Cu, Au, Ag)or alloy thereof, or laminated films thereof. The gate insulating film31 is formed in the upper layer of the gate lines 11 and the commonlines 13, and may be formed of an oxide film, a nitride film, or thelike, for example.

The source line 12 is arranged to be perpendicular to the gate line 11on the gate insulating film 31. The source line 12 has a bendingstructure of a dog-leg shape extended in a vertical direction with amulti-domain pixel structure in order to deal with color shifting, and aplurality of source lines 12 are arranged in a lateral direction (seeFIG. 2). The source line 12 may be formed of a single layer film ofmetal (e.g., Al, Cr, Mo, Ti, Ta, W, Ni, Cu, Au, Ag) or alloy thereof, orlaminated films thereof, for example.

The TFT 20 which serves as a switching element is arranged near theintersection of the gate line 11 with the source line 12. In the TFT 20,a part of the gate electrode 21 is arranged opposite to the sourceelectrode 22 and the drain electrode 23 with the gate insulating film31, the semiconductor film 32, and the ohmic contact film 33 interposedtherebetween. The gate line 11 in which the TFT 20 is formed serves asthe gate electrode 21, and a part extending from the source line 12 inthe TFT 20 serves as the source electrode 22. The gate lines 11 and thesource lines 12 form a plurality of pixel regions 9 arranged in matricesin the display area 3.

The semiconductor film 32 is formed above the gate insulating film 31.The ohmic contact film 33 is laminated onto the semiconductor film 32,and is formed of a layer obtained by implanting impurities into thesemiconductor film 32, for example. The ohmic contact film 33 that isarranged between the source electrode 22 and the drain electrode 23 isremoved, which serves as a channel part. The source electrode 22 and thedrain electrode 23 are formed in the same layer as the source line 12,and are formed on the ohmic contact film 33 so as to overlap thereon.

The transparent pixel electrode 14 is formed in the pixel region 9 in aplate shape (planar shape). The transparent pixel electrode 14 is formedof a transparent conductive film such as an indium tin oxide (ITO) film,or an indium zinc oxide (IZO) film. The transparent pixel electrode 14is formed on the drain electrode 23 so as to be directly overlappedthereon for electrical connection. The transparent pixel electrode 14may be formed in the lower layer of the drain electrode 23 forelectrical connection, or may be formed in the upper layer of the drainelectrode 23 through a contact hole for electrical connection.

A protection film 34 is formed in the upper layer of the source line 12,the source electrode 22, the drain electrode 23, and the transparentpixel electrode 14. The protection film 34 may be a single layer film ofan insulating film (e.g., an oxide film, a nitride film, or an organicresin film), or may be laminated films thereof.

The transparent common electrode 15 is arranged opposite to thetransparent pixel electrode 14 in a predetermined area with theprotection film 34 interposed therebetween. The transparent commonelectrode 15 is formed of a transparent conductive film such as ITO,IZO, or the like. In the transparent common electrode 15, branch-likeelectrode parts 18 electrically connected each other, slit-like gapparts 19 from which the transparent conductive film is removed, and aconnection electrode part 17 connecting the branch-like electrode parts18 are formed. The liquid crystal is driven by generating a fringeelectrical field between the transparent common electrode 15 and thetransparent pixel electrode 14.

By covering substantially all of the gate line 11, the source line 12,the common line 13, and the TFT 20 with the connection electrode part 17and forming a lattice shape of the connection electrode part 17, theresistance of the transparent common electrode 15 may further belowered. Further, even when a part of the common line 13 isdisconnected, the reference potential is supplied to the transparentcommon electrode 15 through the connection electrode part 17, which canprevent a display defect and improve a yield.

Further, since the connection electrode part 17 covers the gate line 11,the source line 12, the common line 13, and the TFT 20, a leakageelectric field to the liquid crystal layer can be shielded. As a result,the display defect due to the leakage electric field that tends to begenerated near the gate line 11, the source line 12, the common line 13,and the TFT 20 can be suppressed.

Note that the connection electrode part 17 is not limited to thestructure above, but may be changed in various ways. For example, theconnection electrode part 17 may be formed only on the gate line 11 andthe source line 12, and the branch-like electrode parts 18 of theadjacent pixel regions 9 may be connected each other.

FIG. 4 shows a schematic cross-sectional view near the source line 12arranged in the display area 3 of the liquid crystal display panel 100according to the first exemplary embodiment. For the sake of convenienceof explanation, FIG. 4 schematically shows only the elements needed forthe explanation, and the transparent pixel electrode 14 and the like arenot shown. FIG. 4 corresponds to a view taken along the line IV-IV ofFIG. 2.

The liquid crystal display panel 100 includes, as shown in FIG. 4,liquid crystal 50 held between the array substrate 1 and the colorfilter substrate 2, transparent substrates 51 and 52, a lower-sidepolarizing plate 53, and an upper-side polarizing plate 54. Thelower-side polarizing plate 53 is arranged in an external principalsurface of the array substrate 1, and the upper-side polarizing plate 54is arranged in an external principal surface of the color filtersubstrate 2. Absorption axes of the upper-side polarizing plate 54 andthe lower-side polarizing plate 53 are arranged so as to beperpendicular to each other.

The cell gap between the array substrate 1 and the color filtersubstrate 2 is set, e.g., as 2 to 5 μm. A color filter 41, a blackmatrix 42, an alignment film (not shown) and the like are arranged onthe color filter substrate 2.

The source lines 12 are formed on the array substrate 1, as describedabove, and the transparent common electrode 15 which is a comb-toothelectrode is arranged in the upper layer of the source lines 12 so as tooverlap with the source lines 12 with the protection film 34 interposedtherebetween. The transparent common electrode 15 above the source lines12 serves to shield the electric field from the source lines 12.Further, an alignment film 61 is formed in the uppermost layer of thearray substrate 1.

As shown in FIG. 4, the black matrix 42 is arranged so as to overlapwith the source line 12 in a plane view above the source line 12. Byproviding the black matrix 42, color mixture in the adjacent pixels canbe prevented. In the first exemplary embodiment, the black matrix 42 isarranged only in a position described below so as to cover the upperpart of the source line 12.

The black matrix 42 includes eaves 43 having a distance D1 on outersides in a width direction of the source line 12. In the first exemplaryembodiment, the distance D1 (overhanging amount) of the eaves 43 is setto be equal to or larger than 3.0 μm. In other words, the width of theblack matrix 42 above the source line 12 is set to be larger than thatof the source line 12 by 6.0 μm or larger. Note that it is not necessarythat the both end parts of the eaves 43 arranged at both ends of theblack matrix 42 in a width direction have the distance D1, but they mayhave different values.

The transparent common electrode 15 is arranged above the source line 12so as to protrude with respect to the black matrix 42 in both ends inthe width direction. Specifically, the widths of both end parts of thetransparent common electrode 15 protrude compared to the end parts ofthe black matrix 42 by a distance D2. In the first exemplary embodiment,each end part of the transparent common electrode 15 protrudes(overhangs) compared to the black matrix 42 by 2.5 μm in both ends inthe width direction.

Next, a manufacturing method of the liquid crystal display panel 100according to the first exemplary embodiment will be described. The arraysubstrate 1 is manufactured by forming the TFT 20, the transparent pixelelectrode 14, the transparent common electrode 15 and the like on onesurface of a glass substrate by repeatedly using a pattern formingprocess including film forming, patterning by photolithography, etchingand the like. The color filter substrate 2 is manufactured by formingthe color filter 41 and the black matrix 42 on one surface of a glasssubstrate.

Next, processes before the array substrate 1 and the color filtersubstrate 2 are attached will be described. First, in a substratecleaning process, the array substrate 1 on which the transparent pixelelectrode 14 is formed is cleaned. Next, in an alignment film materialapplying process, an organic film or the like made of polyimide which isa material of an alignment film is applied on one surface of the arraysubstrate 1 by a printing method, which is then subjected to sinteringprocessing by a hot plate to dry this part. After that, alignmentprocessing is performed on the manufacturing substrate on which thealignment film material is applied. The alignment processing isperformed by rubbing the surface of the alignment film in apredetermined direction by rotating a rubbing roller in which a clothmade of nylon (registered trademark) or the like is rolled whilepressing it at a predetermined pressure. Further, the alignment film ofthe color filter substrate 2 is similarly formed by performingprocessing including cleaning, application of an organic film, andalignment.

FIG. 5 shows a schematic plane view of element parts of the arraysubstrate 1 of the liquid crystal display device according to the firstexemplary embodiment. The array substrate 1 includes, as describedabove, the source lines 12 which are bended in a dog-leg shape. Thetransparent common electrode 15 also includes the branch-like electrodeparts 18 and the gap parts 19 bended in a dog-leg shape in the samedirection as the source lines 12.

When the source lines are formed in a linear shape, the rubbingdirection and the source lines can be made parallel to each other. Inthe first exemplary embodiment, it is advantageous for color shifting.The source line 12 has a dog-leg shape in the first exemplaryembodiment, which cannot parallel the rubbing direction and the sourceline (see FIG. 5). Accordingly, when the rubbing processing isperformed, the rubbing roller 70 ascends or descends the step of thesource line 12 as shown in FIG. 6.

Next, in a sealant applying process to form sealant, resin which issealant is applied to one surface of the array substrate 1 and the colorfilter substrate 2. Thermosetting hard resin such as epoxy adhesive orultraviolet hardening resin is used as the sealant, for example.

The array substrate 1 and the color filter substrate 2 manufacturedaccording to the process above are arranged to be opposite to eachother, and the pixels of the panels formed in the respective substratesare attached by being aligned to correspond with each other. The curingprocessing is performed for curing the sealant to the array substrate 1and the color filter substrate 2 attached in the above way. This processis performed, for example, by applying heat or irradiating it withultraviolet rays according to the material of the sealant.

Next, a thinning polishing process and the like are performed on thetransparent substrate by chemical polishing using chemicals and physicalpolishing to polish the substrate with an abrasive as needed. Next, in acell dividing process, the attached substrate is divided into separatecells corresponding to each of the liquid crystal display panels 100.After the cell dividing process, a liquid crystal implanting process toimplant liquid crystal from a liquid crystal inlet is performed invacuum. Further, in a sealing process, by applying photocurable resin toa liquid crystal inlet and irradiating it with light, the liquid crystalinlet is sealed.

Next, in a polarizing plate attaching process, a polarizing plate isattached to the outside of the array substrate 1 and the color filtersubstrate 2. Subsequently, in a control substrate mounting process, acontrol substrate is mounted, which completes the liquid crystal displaypanel 100. After that, the liquid crystal display panel 100 and thebacklight unit are embedded and held in a housing, which completes theliquid crystal display device. Note that the manufacturing method ismerely an example, and is not limited to the method stated above.

FIG. 7 shows a correlation diagram in which measured values of aluminance at the time of black display in a frontal direction(hereinafter referred to as “black luminance”) are plotted with respectto the distance D1 of the eaves 43 of the black matrix 42 on the sourceline 12. The sample in which the distance D1 is in the range of 0 μm to15 μm is manufactured to perform evaluation. Note that the graph of FIG.7 standardized the black luminance of the following conditions for 1.That is, it is the condition that the source wire 12 and the blackmatrix 42 have the same width and overlap each other in a plane view(i.e., the condition that does not provide the eaves 43 to the blackmatrix 42). Further, each bending angle of the source lines 12, thebranch-like electrode part 18 and the gap part 19 of the transparentcommon electrode 15 in the sample is set as about 10°.

It is shown in FIG. 7 that the black luminance can be suppressed byarranging the eaves 43 in the black matrix 42. Larger value of thedistance D1 of the eaves 43 means higher effect of the suppression ofthe black luminance. Further, it is shown in FIG. 7 that the gradient ofthe distance D1 of the eaves 43 changes when the distance D1 reaches 3.0μm. In short, a change point exists at the distance D1 of 3.0 μm. Morespecifically, when the distance D1 of the eaves 43 is smaller than 3.0μm, the gradient is large, which means it is possible to obtain highereffect of decreasing the black luminance with respect to the increaseamount of the distance D1 of the eaves 43. On the other hand, when thedistance D1 of the eaves 43 is 3.0 μm or larger, the gradient is smallerthan the former case, which means the effect of decreasing the blackluminance with respect to the increase amount of the distance D1 of theeaves 43 is smaller than the former case.

When the distance D1 of the eaves 43 is smaller than 3.0 μm, it can beestimated that the black luminance increases due to both of a lightleakage (see FIG. 8) by the alignment defect of the liquid crystal 50beside the source line 12 and a light leakage of light-scatteringcomponents due to thermal fluctuation of the liquid crystal 50 in thecolor filter opening part. On the other hand, when the distance D1 ofthe eaves 43 is 3.0 μm or larger, it can be estimated that the blackluminance increases only due to the light leakage of light-scatteringcomponents due to the thermal fluctuation of the liquid crystal 50 inthe color filter opening part.

It is experimentally confirmed that the area with the alignment defectnear the source line 12 influences on the black luminance. The reasonwhy the light leakage occurs due to the alignment defect of the liquidcrystal 50 beside the source line 12 is that, since the step of thesource line 12 is typically equal to or larger than 0.1 μm, the defectof the alignment film tends to occur in this area. The defect of thealignment film 61 is considered to occur since the rubbing cloth rolledin the rubbing roller cannot rub the step part of the source line 12 inthe similar way as in other areas due to the step of the source line 12,and the liquid crystal cannot be aligned in a desired direction. As aresult, the alignment defect easily occurs and the black luminance tendsto increase in the liquid crystal beside the source line 12. When metallike chrome is used as a conventional common electrode, the alignmentdefect near the source line is shielded by lines. In this case, such aphenomenon did not occur.

As is clear from FIG. 7, by arranging the eaves 43, the increase in theblack luminance can be suppressed. The first reason is that the presenceof the eaves 43 leads to suppression of the increase in transmissionlight components due to the alignment defect in the liquid crystal 50beside the source line 12 (areas shown in A1 in FIG. 4). The secondreason is that the presence of the eaves 43 can prevent the lightleakage due to dynamic light-scattering components caused by the thermalfluctuation.

However, an excessive increase in the distance D1 of the eaves 43 of theblack matrix 42 leads to a decrease in the opening ratio. This maydecrease the white luminance and reduce the contrast. In other words,the contrast can be improved by preventing the white luminance frombeing greatly decreased. The present inventors have made furtherexamination of the distance D1 of the eaves 43 of the black matrix 42 todecrease the reduction degree of the white luminance.

FIG. 9 shows electrode position dependent calculation data of thetransmission rate when the white display is performed. The calculationis performed using a commercially available simulator (Sintech, Inc.:LCD-Master). It is apparent from FIG. 9 that the transmission ratebecomes high in the vicinity of the edge parts of the transparent commonelectrode 15. It is thus understood that the decrease in the whiteluminance can be suppressed by preventing the edge parts of thetransparent common electrode 15 from being shielded by the black matrix42.

FIG. 10 shows a transmission rate from the end part of the black matrix42 to the edge part of the transparent common electrode 15 with respectto the distance D2. In the graph shown in FIG. 10, the transmission ratewhen the distance D2 from the end part of the black matrix 42 to theedge part of the common electrode 15 is 5 μm is specified as 1.

It is clear from FIG. 10 that the white luminance can be improved byensuring the distance D2 from the end part of the black matrix 42 to theedge part of the transparent common electrode 15. In particular, it isclear that the contrast can be improved more efficiently by setting thedistance D2 as 2.5 μm or larger.

According to the first exemplary embodiment, the transparent conductivefilm is used as both of the transparent pixel electrode 14 and thetransparent common electrode 15, thereby capable of providing a liquidcrystal display device of FFS type with high transmission rate. Further,according to the first exemplary embodiment, it is only required tochange the mask for forming the transparent common electrode and thelight-shielding layer, which does not require introduction of newequipments. It has further advantage that the number of process stepsdoes not increase.

Further, according to the first exemplary embodiment, by providing theblack matrix 42 overlapped with the source line 12 and providing theeaves 43 at both end parts in the width direction of the black matrix42, the increase in the black luminance in the frontal direction can besuppressed. Further, since the transparent common electrode 15 isarranged above the source line 12 to project at both end parts in thewidth direction compared with the black matrix 42, the reduction in thewhite luminance can be suppressed. This is because the high transmissionpart of the edge parts of the transparent common electrode 15 areprevented from being shielded. As a result, the contrast can beimproved.

In addition, according to the first exemplary embodiment, the distanceD1 of the eaves 43 of the black matrix 42 is set to be 3.0 μm or larger.Accordingly, it is possible to suppress the increase in the blackluminance more efficiently. Further, the distance D2 from the edge partof the transparent common electrode 15 to the end part of the blackmatrix 42 is set as 2.5 μm or larger. Accordingly, it is possible tosuppress the decrease in the white luminance more efficiently. As aresult, the contrast can be improved more efficiently.

When the source line is formed in a non-linear shape such as a dog-legshape, the rubbing direction and the source line cannot be madeparallel, which tends to generate the alignment defect of the liquidcrystal beside the source line. The present invention is especiallyeffective for such a configuration.

When the disorder of the alignment of the liquid crystal near the gateline 11, the common line 13, and the TFT 20 becomes a problem, the blackmatrix can be provided also above these lines to provide the eaves. Forexample, when a structure of top-gate type is employed, the black matrixmay be provided to cover the gate line at least above the gate line, andthe eaves may be provided in both end parts of the black matrix. Thesimilar configuration may be employed for the common line.

Described above is the example in which the bending angle of the sourceline 12 and the transparent common electrode 15 is 10°. This is merelyan example, however, and the bending angle may be any desired value.Further, described above is the example in which one bending structureis formed in the source line 12 arranged between the two pixel regions9. However, a plurality of bending structures may be formed. Further,the bending shape may be designed in a desired way. Furthermore, it isneedless to say that the present invention can be applied to the one inwhich the source line 12 has a linear shape. The bending structure maybe provided in the side of the gate line instead of the source line.

Second Exemplary Embodiment

Next, one example of a liquid crystal display device having a structuredifferent from that of the first exemplary embodiment will be described.In the following description, the same element members as those in thefirst exemplary embodiment are denoted by the same reference symbols,and its description will be omitted as appropriate.

Described in the second exemplary embodiment is one example of theliquid crystal display device that aims to improve contrast from anoblique direction in addition to contrast from a frontal direction.

FIG. 11A is an explanatory view of absorption axes of a lower-sidepolarizing plate 53 and an upper-side polarizing plate 54 seen from afrontal direction, and FIG. 11B is an explanatory view of absorptionaxes of the lower-side polarizing plate 53 and the upper-side polarizingplate 54 seen from an oblique direction. When the liquid crystal displaypanel is seen from the frontal direction, the angle of the absorptionaxes of the lower-side polarizing plate 53 and the upper-side polarizingplate 54 is 90° as shown in FIG. 11A, whereas the angle of theabsorption axes of the lower-side polarizing plate 53 and the upper-sidepolarizing plate 54 seen from the oblique direction is larger than 90°as shown in FIG. 11B.

FIG. 12 shows a graph in which contrast is plotted with respect to apolar angle. The one that does not have the eaves 43 of the black matrix42, which means the one in which the black matrix 42 and the source line12 are substantially overlapped (D1=0), and the one in which thedistance D1 of the eaves 43 of the black matrix 42 is 5 μm aremanufactured and used as samples. The polar angle here means, as shownin FIG. 13A, an angle between the viewing direction and the normaldirection of the polarizing plate. Further, an azimuth angle that willbe mentioned later means, as shown in FIG. 13B, an angle between thedirection in which the viewing direction is projected to the upper-sidepolarizing plate 54, and the absorption axis of the upper-sidepolarizing plate 54.

As shown in FIG. 12, with increasing the polar angle (with increasingthe oblique view), it is understood the light leakage increases and thecontrast decreases. More specifically, it is empirically confirmed that,at the azimuth angle 45°, when the angle is an oblique view of the polarangle of 30° or larger, the light leakage due to the oblique view islarger than the light leakage due to the alignment defect near thesource line 12, which loses the effect of the distance D1 of the eaves43 of the black matrix 42.

The present inventors have thus examined the structure to increase thecontrast not only in the frontal direction but also in the oblique view.As a result, it is turned out that the light leakage due to thepolarizing plate can be suppressed by adding a two-axis phase differencefilm between the polarizing plate (polarizer) and the liquid crystal.Note that a polarizing plate with a two-axis phase difference film maybe used. In this case, the polarizer is arranged in the outer side.

FIG. 14 shows a schematic cross-sectional view of the liquid crystaldisplay device according to the second exemplary embodiment. A liquidcrystal display panel 100 a includes a lower-side polarizing plate 53,and an upper-side polarizing plate 54. A two-axis phase difference film55 is arranged between the lower-side polarizing plate 53 and thetransparent substrate 51 forming the array substrate 1. Further, atwo-axis phase difference film 56 is arranged between the upper-sidepolarizing plate 54 and the transparent substrate 52 forming the colorfilter substrate 2. In the second exemplary embodiment, a polarizingplate with NAZ film Nz=0.3, Δnd=180 nm manufactured by Nitto DenkoCorporation is used as the two-axis phase difference film 55 and thelower-side polarizing plate 53, and the two-axis phase difference film56 and the upper-side polarizing plate 54. Needless to say, it is notlimited to this, but other two-axis phase difference films may bepreferably used.

The light leakage due to the alignment defect near the source line 12 isthe dominant factor of the black luminance from the oblique direction,which gives an adverse effect. Thus, the correlation of the contrast andthe distance D1 of the eaves 43 of the black matrix 42 is examined alsofor the black luminance of the oblique direction view.

FIG. 15 shows a graph in which the relative contrast from a viewingdirection of the azimuth angle of 45°, polar angle of 45° is plottedwith respect to the distance D1 in the liquid crystal display device ofthe second exemplary embodiment. As a result, it is confirmed that thecontrast in the direction of the oblique view can be improved by addingthe two-axis phase difference films 55 and 56 and providing the eaves 43of the black matrix 42. Further, it is turned out that the contrast inthe oblique direction can be improved with more efficiency by settingthe distance D1 as 2.5 μm or larger.

According to the second exemplary embodiment, it is possible to achievethe improvement of the contrast not only in the frontal direction butalso in the oblique direction by adding the two-axis phase differencefilm between the polarizing plate and the liquid crystal.

Described in the second exemplary embodiment is the example in which twotwo-axis phase difference films are provided. However, the similareffect as that described above can be obtained also by providing thetwo-axis phase difference film only in one of the upper-side polarizingplate 54 and the lower-side polarizing plate 53.

Third Exemplary Embodiment

A basic structure of a liquid crystal display device according to athird exemplary embodiment is similar to that of the first exemplaryembodiment except the following point. The third exemplary embodimentdiffers from the first exemplary embodiment in that source lines and atransparent common electrode are made in a linear shape.

FIG. 16 shows a schematic plane view of a main part of an arraysubstrate 1 b of the liquid crystal display device according to thethird exemplary embodiment. The array substrate 1 b includes a sourceline 12 b that is formed in a linear shape. Further, as is similar tothe source line 12 b, a transparent common electrode 15 b includesbranch-like electrode parts 18 b and gap parts 19 b which are made in alinear shape.

It is considered that the reason why the light leakage occurs due to thealignment defect of the liquid crystal 50 beside the source line 12 b isthat, since the step of the source line 12 b is typically 0.1 μm orlarger, the defect of the alignment film easily occurs in the area. Thedefect of the alignment film 61 is considered to occur since the rubbingcloth rolled in the rubbing roller cannot rub the step part in thesimilar way as in other areas due to the step of the source line 12 b,and the liquid crystal cannot be aligned in a desired direction. As aresult, the alignment defect easily occurs and the black luminance tendsto increase in the liquid crystal beside the source line 12.

According to the third exemplary embodiment, the same effect as that inthe first exemplary embodiment can be obtained. In particular, when thestep of the source line is large, the condition at the time of rubbingis different between the neighborhood of the step structure and otherareas, which easily causes the alignment defect of the liquid crystal.The present invention is particularly effective in such a structure.

Note that the liquid crystal display panel and the liquid crystaldisplay device according to the present invention are not limited to theexemplary embodiments described above, but may be changed as appropriatewithout departing from the spirit of the present invention. Furthermore,the above first exemplary embodiment to the third exemplary embodimentmay be suitably combined.

Described in the exemplary embodiments above is an example of providingthe transparent common electrode and the black matrix on the sourcelines. However, it is not limited to the source line. A transparentcommon electrode and a black matrix having the following structures canbe applied to the conductive pattern in the display area 3 in which thelight leakage occurs due to the alignment defect of the liquid crystal.Specifically, a light-shielding layer provided to overlap with theconductive pattern in a planar view and including eaves protrudingcompared with the conductive pattern may be formed. The transparentcommon electrode may be arranged to cover the conductive pattern and toprotrude compared to the light-shielding layer. By applying thesestructures, the similar effect as that in the exemplary embodimentsabove can be obtained. The conductive pattern includes, for example, agate line, a common line, and a TFT.

When the gate lines are arranged above the source lines (e.g., top-gatetype), the transparent common electrode and the black matrix asdescribed above are arranged on the gate lines, thereby achieving thesimilar effect as that in the exemplary embodiments described above.

The transparent common electrode which is the comb-tooth electrode mayat least have a gap part and a branch-like electrode part, and it mayhave any shape. The shape of the source line and the gate line is merelyan example, and various other shapes may be used.

Further, although described above is the example of rubbing thealignment film, the present invention is not limited to the alignmentprocessing method by the rubbing processing but the alignment processingmay be performed by other processing like a photo-alignment method.Further, the transparent conductive film is not limited to ITO, IZO, andvarious materials can be used.

Although the example of the black matrix has been described as thelight-shielding layer, other materials may be used without departingfrom the spirit of the present invention as long as it has alight-shielding function. A parallax barrier or the like may be used asthe light-shielding layer. Further, the arrangement of thelight-shielding layer is not particularly limited. For example, thelight-shielding layer may be provided on the external principal surfaceof the color filter substrate or may be provided on the side of thearray substrate.

From the invention thus described, it will be obvious that the exemplaryembodiments of the invention may be varied in many ways. Such variationsare not to be regarded as a departure from the spirit and scope of theinvention, and all such modifications as would be obvious to one skilledin the art are intended for inclusion within the scope of the followingclaims.

1-8. (canceled)
 9. A liquid crystal display panel including a firstsubstrate, a second substrate and liquid crystal interposed between thefirst and the second substrates, wherein the first substrate comprises:a conductive pattern that is at least one of a gate line, a source lineformed to cross the gate line, and a common line; a switching elementthat is arranged near the intersection of the gate line and the sourceline; a transparent pixel electrode that is connected to the switchingelement; an insulating layer formed on the transparent pixel electrodeand the conductive pattern; and a transparent common electrode arrangedon the insulating layer and facing to the conductive pattern through theinsulating layer, the transparent common electrode including a firstflat portion above the conductive pattern, a step portion near the edgeof the conductive pattern and a second flat portion extending from thefirst flat portion through the step portion, and wherein the secondsubstrate comprises a shielding layer overlapping at least the stepportion of the transparent common electrode, the edge of the shieldinglayer positioned at outer portion than the step portion of thetransparent common electrode and inner portion than the edge of thesecond flat portion of the transparent common electrode in the planeview.
 10. A liquid crystal display panel according to claim 9, whereinthe edge of the shielding layer protrudes by 3.0 μm or larger from theedge of the conductive pattern in the plane view.
 11. A liquid crystaldisplay panel according to claim 9, wherein the both edges of theshielding layer protrude from the edges of the conductive pattern in theplane view.
 12. A liquid crystal display panel according to claim 9,wherein the transparent common electrode protrudes from the edge of theshielding layer by 2.5 μm or larger in the plane view.
 13. A liquidcrystal display panel according to claim 9, wherein the transparentcommon electrode protrudes from both the edges of the shielding layerfacing each other in the plane view.
 14. A liquid crystal display panelaccording to claim 9, wherein the shielding layer overlaps with thefirst flat portion, the step portion, and the part of the second flatportion of the transparent common electrode.
 15. A liquid crystaldisplay panel according to claim 9, wherein the shielding layer is blackmatrix.
 16. A liquid crystal display panel according to claim 9, whereinthe transparent common electrode includes at least branch-like electrodeparts and gap parts between the branch-like electrodes.
 17. A liquidcrystal display panel according to claim 9, wherein a first polarizingplate including a polarizer is arranged in an external principal surfaceof the first substrate, a second polarizing plate including a polarizeris arranged in an external principal surface of the second substrate,and a two-axis phase difference film is arranged in at least one of anarea between the polarizer of the first polarizing plate and the liquidcrystal and an area between the polarizer of the second polarizing plateand the liquid crystal.
 18. A liquid crystal display panel according toclaim 9, wherein the conductive pattern and the transparent commonelectrode formed above the conductive pattern have a bending structure.19. A liquid crystal display panel according to claim 9, wherein theliquid crystal is driven by a fringe electric field.
 20. A liquidcrystal display device on which the liquid crystal display panelaccording to claim 9 and a backlight unit are mounted.
 21. A liquidcrystal display panel including a first substrate, a second substrateand liquid crystal interposed between the first and the secondsubstrates, the liquid crystal driven by a fringe electric field,wherein the first substrate comprises: a conductive pattern that is atleast one of a gate line, a source line formed to cross the gate line,and a common line; a switching element that is arranged near theintersection of the gate line and the source line; a transparent pixelelectrode that is connected to the switching element; an insulatinglayer formed on the transparent pixel electrode and the conductivepattern; and a transparent common electrode arranged on the insulatinglayer and facing to the conductive pattern through the insulating layer,the transparent common electrode including a first flat portion abovethe conductive pattern, a step portion near the edge of the conductivepattern and a second flat portion extending from the first flat portionthrough the step portion, and wherein the second substrate comprises ashielding layer overlapping the first flat portion, the step portion,and a part of the second flat portion of the transparent commonelectrode.
 22. A liquid crystal display panel according to claim 21,wherein the shielding layer protrudes by 3.0 μm or larger from the edgeof the conductive pattern in the plane view.
 23. A liquid crystaldisplay panel according to claim 21, wherein the transparent commonelectrode protrudes from the end edge of the shielding layer by 2.5 μmor larger in the plane view.
 24. A liquid crystal display panelaccording to claim 22, wherein the transparent common electrodeprotrudes from the end edge of the shielding layer by 2.5 μm or largerin the plane view.
 25. A liquid crystal display panel according to claim21, wherein the shielding layer is black matrix.
 26. A liquid crystaldisplay device on which the liquid crystal display panel according toclaim 21 and a backlight unit are mounted.
 27. A liquid crystal displaypanel including a first substrate, a second substrate and liquid crystalsealed between the first and the second substrates, the liquid crystaldriven by a fringe electric field, wherein the first substratecomprises: a gate line; a source line which includes a bending structureand is formed to cross the gate line; a switching element that isarranged near the intersection of the gate line and the source line; atransparent pixel electrode that is connected to the switching element;an insulating layer formed on the transparent pixel electrode and thesource line; and a transparent common electrode includes at leastbending branch-like electrode parts and gap parts between the bendingbranch-like electrodes and faces to the source line through theinsulating layer, the transparent common electrode including a firstflat portion above the source line, a step portion near the edge of thesource line and a second flat portion extending from the first flatportion through the step portion, and wherein the second substratecomprises a black matrix overlapping the first flat portion, the stepportion, and a part of the second flat portion of the transparent commonelectrode.
 28. A liquid crystal display device on which the liquidcrystal display panel according to claim 27 and a backlight unit aremounted.